JP2005010746A - Image forming apparatus and color shift correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten time required for the color shift correcting operation of an image forming apparatus that forms a color image by superimposing images of respective colors. <P>SOLUTION: A control means 101 repeatedly executes control in which color registration marks are formed on an intermediate transfer belt, an amount of correction of misregistration between color images is obtained based upon a positional relation between the registration marks detected by a registration sensor 43 and the position of the formation of each image is corrected based upon the amount of correction of the misregistration. In this case, during the obtained amount of correction of the misregistration is not within a target range, the position of the formation of each image is corrected per pixel. When the amount of correction of the misregistration falls within the target range, the position of the formation of each image is corrected including an amount of correction which is less than a pixel unit, and a series of corrections is ended. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms a color image by superimposing a plurality of images of each color, and a color misregistration correction method thereof.

  2. Description of the Related Art Conventionally, there are image forming apparatuses such as a color copying machine and a color printer that form and output a color image by superimposing yellow (Y), magenta (M), cyan (C), and black (K) images. .

  For example, in a tandem color copier using an electrophotographic process, an image forming unit including a photosensitive drum, a charging device, a scanning optical device, and a developing device is prepared for each color, and these are formed as an endless belt-shaped intermediate unit. A color image is formed by superimposing images of the respective colors on an intermediate transfer belt that is arranged along the transfer belt and circulates. The color image formed on the intermediate transfer belt is transferred to transfer paper and output.

  When a color image is formed by superimposing the images of the respective colors as described above, a color shift occurs and a beautiful image cannot be obtained unless the image formation positions exactly match the colors. Therefore, a test image for correcting color misregistration called a registration mark is formed on the intermediate transfer belt, and this is read by an optical sensor to obtain a necessary correction amount to correct the image forming position.

  The correction amount obtained by creating and measuring the registration mark includes a fine correction amount smaller than a pixel unit. Of these, correction in units of pixels in the main scanning direction is realized by adjusting the timing at which an image signal is supplied to the laser diode of the scanning optical device in units of clocks. Correction of less than a pixel unit in the main scanning direction is performed, for example, by controlling the phase of a polygon mirror that scans laser light in the width direction of the photosensitive member.

  In the color misregistration correction operation, a process of creating a registration mark, measuring it, deriving a necessary correction amount, and performing both pixel unit correction and pixel unit correction according to the correction amount is performed. Repeatedly, the amount of color misregistration is driven within an allowable range.

JP-A-6-95474

  The correction in units of pixels is completed in a short time because the timing for applying the image signal to the laser diode is only adjusted in units of clocks. On the other hand, the surface phase control of the polygon mirror that corrects less than a pixel unit requires a long time (several seconds) until the rotation of the polygon mirror is stabilized after the phase is adjusted. Conventionally, both the correction of less than a pixel unit that requires a long time and the correction of a pixel unit that ends in a short time are performed every time a registration mark is created and measured and corrected. There is a problem that the period from creation to the next registration mark creation becomes longer, and it takes a long time to complete a series of correction operations.

  The present invention has been made paying attention to such problems of the prior art, and shortens the time required for color misregistration correction operation in an image forming apparatus that forms a color image by superimposing images of respective colors. It is an object.

  The gist of the present invention for achieving the object lies in the inventions of the following items.

The invention according to claim 1 is provided with a plurality of image forming means for forming images of different colors, and forming a color image by superimposing a plurality of images of each color formed on the same image forming medium. In the device
A test image creating means for creating a test image on the image forming medium for correcting a positional deviation between the images of the respective colors;
A correction amount deriving unit that measures a test image created on the image forming medium and derives a displacement correction amount between the images of the respective colors;
Correction means for correcting the image forming position by each of the image forming means;
Control means for controlling a series of correction operations for correcting the positional deviation between the images of the respective colors,
The control means performs the correction operation in a first stage and a second stage thereafter, and corrects the positional deviation in units of pixels until the positional deviation correction amount enters a predetermined target range in the first stage. In the image forming apparatus, the positional deviation is corrected including a correction amount less than a pixel unit in the second stage.

  According to the above invention, the operation for correcting the positional deviation of each color image is divided into a first stage for correcting the positional deviation on a pixel basis and a second stage for correcting the positional deviation including a correction amount less than a pixel unit. To be implemented. If the amount of misalignment falls within the target range by creating and measuring a test image, deriving the necessary correction amount, and performing the correction many times, the misalignment amount falls within the target range. There is no need to make fine adjustments as described above, and the target can be achieved only by making detailed adjustments for the final finishing. Therefore, by performing the correction including less than a pixel unit only in the second stage, it is possible to efficiently correct the positional deviation of each color image in a short time. In the second stage, in addition to performing only correction in units of pixels, both correction in units of pixels and correction in units of pixels may be performed.

According to a second aspect of the present invention, in the first stage, the control means performs creation and measurement of the test image to derive a correction amount, and the second stage is not processed in the first stage. The image forming apparatus according to claim 1, wherein the correction is performed based on a correction amount remaining in the image forming apparatus.

  According to the above invention, in the second stage, the test image is generated and measured again, and the correction amount is not derived, and the correction amount remaining without being processed in the first step is used. The time required until is reduced. When the positional deviation correction amount acquired at the end of the first stage is within the target range, the pixel unit correction and the pixel unit are performed in the second stage without performing the pixel unit correction in the first stage thereafter. You may comprise so that both of less than correction | amendment may be implemented in parallel.

The invention according to claim 3 is provided with a plurality of image forming means for forming images of different colors, and forming a full color image by superimposing a plurality of images of each color formed on the same image forming medium. In the device
A test image creating means for creating a test image on the image forming medium for correcting a positional deviation between the images of the respective colors;
A correction amount deriving unit that measures a test image created on the image forming medium and derives a displacement correction amount between the images of the respective colors;
Correction means for correcting the image forming position by each of the image forming means;
Control means for controlling a series of correction operations for correcting the positional deviation between the images of the respective colors,
The control means repeatedly creates and measures a test image and derives a misregistration correction amount and then corrects the image formation position based on the derived misregistration correction amount, and the derived misregistration correction amount is within a predetermined target range. Image formation is characterized in that image misalignment is corrected in units of pixels while the image is not within the range, and when the amount of misalignment correction is within the target range, the image formation position is corrected including a correction amount less than the unit of pixels. Device.

  According to the above invention, while the derived misregistration correction amount is not within the target range, the test image is created and measured again after correcting the misregistration of each color image for each pixel. When the misalignment correction amount falls within the target range, correction including a correction amount less than a pixel unit is performed. In the convergence process until the positional deviation correction amount falls within the target range, the correction is performed in units of pixels, so that the positional deviation correction of each color image can be performed efficiently and in a short time.

According to a fourth aspect of the present invention, the control means creates the test image, measures the test image, derives the misregistration correction amount, and calculates the image while the misregistration correction amount is not within the target range. The image forming apparatus according to claim 3, wherein the positional deviation of the image is corrected in units of pixels by repeating correction of a forming position.

The invention according to claim 5 is characterized in that the control means executes correction including a correction amount less than the pixel unit and ends a series of correction operations. Device.

  According to the above invention, after the misalignment correction amount enters the target range, the test image is not created or measured, and correction including less than a pixel unit is performed, and the series of correction operations is completed. As described above, only the correction in units of pixels is performed while the test image is repeatedly created and measured, and the correction including less than the unit of pixels is performed only once at the end of the correction operation. It is possible to carry out efficiently and in a short time.

The invention according to claim 6 is the image forming apparatus according to claim 1, wherein the time required for correction in pixel units is shorter than the time required for correction in less than pixel units. is there.

  According to the above invention, even when the pixel unit correction accompanied by the creation / measurement of the test image is repeatedly performed until the misalignment correction amount enters the target range, the correction time for the pixel unit is short. The operation until completion can be performed in a short time.

The invention according to claim 7 is the image forming apparatus according to claim 1, 2, 3, 4, 5 or 6, wherein correction less than a pixel unit is performed by surface phase control of a polygon mirror.

  According to the above invention, it is possible to finely correct less than a pixel unit.

The invention according to claim 8 is provided with a plurality of image forming means for forming images of different colors, and forming a color image by superimposing a plurality of images of each color formed on the same image forming medium. In the color misregistration correction method in the apparatus,
The correction of color misregistration is performed in the first stage and the subsequent second stage, and in the first stage, the misregistration is corrected in units of pixels until the misregistration correction amount between the images of the respective colors falls within a predetermined target range. In the second step, the color misregistration correction method includes correcting the misregistration including a misregistration correction amount less than a pixel unit.

  According to the above invention, the positional deviation correction of each color image is performed in the first stage for correcting the positional deviation for each pixel and the second stage for correcting the positional deviation including the correction amount less than the pixel unit. . Only after the necessary misregistration correction amount has converged until it has entered the target range, fine adjustment including the correction amount less than the pixel unit is performed, so that misregistration correction of each color image can be performed efficiently and in a short time. .

The invention according to claim 9 is provided with a plurality of image forming means for forming images of different colors, and an image formation for forming a color image by superimposing a plurality of images of each color formed on the same image forming medium In the color misregistration correction method in the apparatus,
Creating a test image on the image forming medium for correcting misregistration between images of each color; measuring the test image; and deriving a misregistration correction amount between the images of each color; Repetitively performing in this order until the positional deviation correction amount falls within a target range, correcting the positional deviation between the images of the respective colors on a pixel basis based on the positional deviation correction amount;
And a step of correcting misregistration between the images of the respective colors including misregistration less than a pixel unit when the misregistration correction amount falls within a target range.

  According to the above-described invention, while the derived misregistration correction amount is not within the predetermined target range, the misregistration of each color image is corrected for each pixel, and then the test image is created and measured again. When the amount enters the target range, correction including a correction amount less than a pixel unit is performed. In the convergence process until the misregistration correction amount falls within the target range, the correction is performed in units of pixels, so that the misregistration correction of each color image can be completed efficiently and in a short time.

The invention according to claim 10 is the color misregistration correction method according to claim 8 or 9, characterized in that the time required for correction in units of pixels is shorter than the time required for correction in units of pixels.

The invention according to an eleventh aspect is the color misregistration correction method according to any one of the eighth to tenth aspects, wherein the correction of less than a pixel unit is performed by the surface phase control of the polygon mirror.

  According to the image forming apparatus and the color misregistration correction method of the present invention, the misregistration is corrected in units of pixels until the misregistration correction amount of each color image enters the target range, and the correction less than the pixel unit is performed after entering the target range. Since the misregistration including the amount is corrected, the misregistration of each color image can be corrected efficiently and in a short time, and the waiting time of the user is shortened.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 shows a cross-sectional configuration of the image forming apparatus 10 according to the embodiment of the present invention. The image forming apparatus 10 is an apparatus called a color digital copying machine. The image forming apparatus 10 includes an automatic document feeder 20, a reading unit 30, and a printer unit 40. The automatic document feeder 20 has a function of feeding the documents 2 stacked on the document placing tray 21 one by one to the reading portion of the reading unit 30 and discharging the read documents to the discharge tray 27. The double-sided document has a function of reversing the front and back and sending it to the reading unit 30 after single-sided scanning.

  The automatic document feeder 20 includes a paper feed roller 22 that sequentially feeds the documents stacked on the document placing tray 21 from the top, and a contact roller for allowing the document to pass while contacting the contact glass 31 that is a document reading position. 23 and a guide roller 24 for guiding the original fed by the paper feed roller 22 along the contact roller 23. Further, a switching claw 25 for switching the advancing direction of the document that has passed through the contact glass 31, a reversing roller 26 for reversing the front and back of the double-sided document, and a paper discharge tray 27 for discharging the document that has been read are provided. Yes.

  The reading unit 30 has a function of reading a document in color. The reading unit 30 includes an exposure scanning unit 35 including a light source 33 and a mirror 34, a color line image sensor 36 that receives reflected light from a document and outputs an electrical signal corresponding to the light intensity, and a document. A condenser lens 37 that condenses the reflected light from the line image sensor 36, and various mirrors 38 that form an optical path for guiding the reflected light from the mirror 34 of the exposure scanning unit 35 to the line image sensor 36. ing.

  When reading a document fed by the automatic document feeder 20, the exposure scanning unit 35 moves to a reading position below the contact glass 31, stops, and reads a moving document conveyed by the contact roller 23 thereon. It is like that. When reading a document placed on the platen glass 32, the exposure scanning unit 35 moves from left to right along the lower surface of the platen glass 32 to read a stationary document.

  The printer unit 40 is called a tandem color image forming apparatus. The printer unit 40 is an endless belt-shaped intermediate transfer belt 41 and a plurality of image forming units 50Y and 50M that respectively form single-color images on the intermediate transfer belt 41. , 50C, 50K, paper feeding means 70 for feeding the transfer paper, transport means 80 for feeding the fed transfer paper, and a fixing device 42. In addition, a control circuit 90 that controls the operation of the entire image forming apparatus is provided.

  The image forming unit 50Y forms a yellow (Y) color image on the intermediate transfer belt 41, and the image forming unit 50M forms a magenta (M) color image on the intermediate transfer belt 41. The image forming unit 50 </ b> C forms a cyan (C) color image on the intermediate transfer belt 41, and the image forming unit 50 </ b> K forms a black (K) color image on the intermediate transfer belt 41.

  The image forming unit 50Y includes a photosensitive member 51Y as a cylindrical electrostatic latent image carrier on which an electrostatic latent image is formed, a charging device 52Y disposed around the photosensitive member 51Y, a developing device 53Y, and a cleaning device. 54Y. In addition, a laser unit 55Y including a laser diode, a polygon mirror, various lenses, a mirror, and the like is provided.

  The photoconductor 51Y is driven by a drive unit (not shown) and rotates in a certain direction (the direction of arrow A in the figure), and the charging device 52Y uniformly charges the photoconductor 51Y. As shown in FIG. 3, the laser unit 55Y reflects the laser light emitted from the laser diode 56Y with a rotating polygon mirror 57Y, thereby causing the surface of the photoreceptor 51Y to be irradiated with laser light in the width direction (main scanning direction). It performs the function of scanning repeatedly. An electrostatic latent image is formed on the photoconductor 51Y by scanning the uniformly charged surface of the photoconductor 51Y with a laser beam that is turned ON / OFF according to yellow image data. The developing device 50Y visualizes the electrostatic latent image on the photoreceptor 51Y with yellow toner. The toner image formed on the surface of the photoreceptor 51 </ b> Y is transferred to the intermediate transfer belt 41 at a location where it contacts the intermediate transfer belt 41. The cleaning device 54Y functions to remove and collect the toner remaining on the surface of the photoreceptor 51Y after being transferred by rubbing with a blade or the like.

  The image forming unit 50M, the image forming unit 50C, and the image forming unit 50K are different from each other in the color of the toner and the image forming unit 50Y except that the laser light is turned on / off with the image data corresponding to each color. The description is omitted here. Note that the same constituent elements have the same numerals and are denoted by M, C, and K instead of the subscript Y.

  The intermediate transfer belt 41 is rotatably supported by winding a plurality of rollers. The intermediate transfer belt 41 circulates in a direction indicated by an arrow B by a driving unit (not shown). In the course of rotation, images of the respective colors are formed on the intermediate transfer belt 41 in the order of (Y), (M), (C), and (K) by the image forming units 50Y, 50M, 50C, and 50K to form a color image. Is synthesized. This color image is transferred from the intermediate transfer belt 41 to the transfer paper at the secondary transfer location C provided at the lower end of the circulation path of the intermediate transfer belt 41.

  A pair of registration sensors 43 a and 43 b made of a reflection type optical sensor for detecting an image formed on the intermediate transfer belt 41 is disposed downstream of the secondary transfer portion C in the circumferential direction. The two registration sensors 43 a and 43 b are disposed apart from each other in the width direction of the intermediate transfer belt 41. A cleaning device 44 for removing toner remaining on the intermediate transfer belt 41 after the transfer is installed further downstream of the registration sensors 43a and 43b.

  The paper feed means 70 has a plurality of paper feed cassettes 71 and normally accommodates transfer papers of different sizes and paper types. The transfer paper accommodated in each paper feed cassette 71 is sent out one by one from the top to the conveying means 80 by the first paper feed roller 72. The conveying unit 80 passes the secondary transfer point C and the fixing device 42 through the secondary transfer portion C and the fixing device 42 and discharges the transfer paper from the paper feeding cassette 71 to the discharge tray outside the apparatus, and the transfer paper passing through the fixing device 42. After reversing the display, the reversing path 80b is formed upstream of the secondary transfer location C and joined again to the normal path 80a. Each of the paths 80a and 80b has a large number of conveying rollers 81 at an interval shorter than the transfer direction size of the minimum size transfer paper.

  The image forming apparatus 10 has a correction operation execution function for adjusting a color image formed on the intermediate transfer belt 41 so as not to cause a color shift. FIG. 4 shows a schematic configuration of a portion related to the correction operation. In the color misregistration correction operation, a test image for color misregistration correction called a registration mark is formed on the intermediate transfer belt 41, which is read by the registration sensors 43a and 43b to determine the correction amount, and the formation position of each color image is corrected. Is done.

  The data processing system 100 is included in the control circuit 90 and controls the image forming units 50Y, 50M, 50C, and 50K to form registration marks on the intermediate transfer belt 41, and uses the registration sensors 43a and 43b to perform registration. In addition to the function of detecting the position of the mark and calculating and deriving the correction amount, it functions to control the overall flow of the correction operation. The correction units 110Y, 110M, 110C, and 110K function to adjust the formation positions when the corresponding image forming units 50Y, 50M, 50C, and 50K form images on the intermediate transfer belt 41, respectively. The correction means 110Y, 110M, 110C, and 110K have a function of adjusting the head position of each line in units of clocks (that is, in units of pixels) when the laser light is turned on / off according to image data, and the surface of the polygon mirror. It has a function of adjusting the head position of each line at a level less than a pixel unit by phase control.

  FIG. 1 shows a schematic configuration of the data processing system 100 and correction means 110Y, 110M, 110C, and 110K. Here, a circuit portion for correcting a positional deviation of each color image in the main scanning direction is shown. The data processing system 100 includes a CPU as a main part, and includes functions of a control unit 101, a test image creation unit 102, a position detection circuit 103, and a correction amount deriving unit 104. The control unit 101 has a function of controlling a series of correction operations for correcting the positional deviation between the images of the respective colors. The test image creating unit 102 creates registration marks on the intermediate transfer belt 41 by controlling the image forming units 50Y, 50M, 50C, 50K and the like. The position detection circuit 103 reads registration marks created on the intermediate transfer belt 41 with the registration sensors 43a and 43b, and is a position that is a correction amount of the formation position of each color image necessary to eliminate color misregistration between the color images. A deviation correction amount is derived. The misregistration correction amount is derived by dividing it into a pixel unit correction amount and a pixel unit correction amount.

  The Y color correction unit 110Y is a circuit that corrects the formation position of the Y color image formed on the intermediate transfer belt 41 by the image forming unit 50Y. The correcting unit 110Y includes a less than pixel unit correcting unit 111Y and a pixel unit correcting unit 112Y. The less-pixel correction unit 111Y is a circuit that generates a polygon CLK121Y that is a clock signal to be supplied to a motor that drives the polygon mirror 57Y of the laser unit 55Y. The less-pixel correction unit 111Y has a function of adjusting the phase of the polygon CLK121Y based on the surface phase control signal 122Y supplied from the data processing system 100.

  The pixel unit correction unit 112Y is a circuit that generates an LD drive signal 123Y for ON / OFF control of the laser diode 56Y of the image forming unit 50Y. The pixel unit correction unit 112Y receives a CLK signal 124 that is a reference for timing of turning on / off the laser diode 56Y in units of pixels, an image signal 125Y that is Y-color image data, and a corresponding laser beam in the main scanning direction. An H-START signal 126Y indicating the timing of crossing the reference position is input.

  The main scanning position correction signal 127Y input from the data processing system 100 represents the timing for starting the ON / OFF control of the LD drive signal 123Y according to the image signal 125Y with reference to the H-START signal 126Y. . For example, the main scanning position correction signal 127Y represents the number of clocks from when the H-START signal 126Y is input until the laser light ON / OFF control is started. The pixel unit correction unit 112Y has a function of adjusting the main scanning direction position of the Y color image formed on the intermediate transfer belt 41 in units of pixels in accordance with the value of the main scanning position correction signal 127Y input from the data processing system 100. It has.

  The M color correcting unit 110M is a circuit that corrects the formation position of the M color image formed on the intermediate transfer belt 41 by the image forming unit 50M. The C color correcting unit 110C is a circuit that corrects the formation position of the C color image formed on the intermediate transfer belt 41 by the image forming unit 50C. The K color correcting unit 110K is the image forming unit 50K that is used by the intermediate transfer belt. 41 is a circuit that corrects the formation position of a K-color image formed on 41. These configurations are the same as those of the Y color correction unit 110Y, and a description thereof will be omitted. The data processing system 100 adjusts the values of the surface phase control signals 122Y, 122M, 122C, and 122K and the main scanning position correction signals 127Y, 127M, 127C, and 127K to be given to the correction units 110Y, 110M, 110C, and 110K. The position of the image in the main scanning direction can be individually controlled.

  FIG. 5 shows an example of a state where the surface phase of the polygon mirror is controlled. The polygon mirror 57Y of the Y color image forming unit 50Y rotates while maintaining the phase difference of the angle θ with respect to the polygon mirror 57K of the K image forming unit 50K. By finely changing the angle θ, the image forming position of less than a pixel unit in the main scanning direction is adjusted.

  FIG. 6 shows an example of a registration mark formed on the intermediate transfer belt 41. The registration mark includes a K-color registration mark 200K, a C-color registration mark 200C, an M-color registration mark 200M, and a Y-color registration mark 200Y. The registration marks 200Y, 200M, 200C, and 200K for each color have a zigzag pattern in which line elements in the width direction and oblique line elements of the intermediate transfer belt 41 appear alternately (four times in the figure). The registration marks 200Y, 200M, 200C, and 200K are formed separately in the vicinity of the left and right ends in the width direction of the intermediate transfer belt 41, and are detected by registration sensors 43a and 43b that are respectively disposed at corresponding positions.

  FIG. 7 shows a state in which the positional deviation and lateral magnification of each color image are detected by the registration mark. For example, the K color based on the length of time T1 from the detection of the width-direction first line element 211K of the K-color registration mark 200K to the detection of the width-direction first line element 211C of the C-color registration mark 200C. The positional relationship in the sub-scanning direction between the first image and the C color image is grasped. Due to the relationship between the time T2 from the detection of the diagonal first line element 212K of the K-color registration mark 200K until the detection of the diagonal first line element 212C of the C-color registration mark 200C, and the previously detected time T1 The positional relationship between the K color image and the C color image in the main scanning direction can be grasped. For example, if T1 = T2, there is no position shift in the main scanning direction. When T2 is shorter than T1 as indicated by Ta in the figure, it can be seen that the C-color image 220 is displaced to the left from the K-color image as indicated by the broken line in the figure. Further, the positional deviation amount can be grasped from the time difference between T1 and Ta.

  In addition, the time when the left registration sensor 43a detects the first line element 211K in the width direction of the left column of the K-color registration mark 200K and the right registration sensor 43b detected the first line element 211KR in the width direction of the right column. The skew (tilt) of the K color image is detected from the difference (T3) from the time. Also, the difference between the time when the left registration sensor 43a detects the diagonal first line element 212K in the left column of the K-color registration mark 200K and the time when the right registration sensor 43b detects the diagonal first line element 212KR in the right column. From the difference between (T4) and the previous (T3), the leveling rate of the K color image is detected. Misregistration, skew, and magnification are similarly detected for other colors.

  FIG. 8 shows a flow of a series of correction operations controlled by the control means 101 of the data processing system 100. The correction operation is performed in a first stage and a second stage. If the color misregistration amount is finally within the target range, the target of the correction operation will be achieved, so fine adjustment as less than a pixel unit is not necessary in the process of converging the color misregistration amount and should be performed only at the final finishing. That's fine. Therefore, in the first stage before the positional deviation correction amount enters the target range, the positional deviation (color deviation) of each color image is corrected in pixel units, and in the second stage after entering the target range, the correction amount less than the pixel unit. Amendment including this is implemented.

  In the first stage of the correction operation, the image forming units 50Y, 50M, 50C, and 50K are controlled to create registration marks for the respective colors on the photoconductors 51Y, 51M, 51C, and 51K (step S301), and these are transferred to the intermediate positions. The registration marks 200Y, 200M, 200C, and 200K shown in FIG. 6 are created on the transfer belt 41 (step S302). These registration marks 200Y, 200M, 200C, and 200K are read by the registration sensors 43a and 43b (step S303), and the correction amount deriving means 104 of the data processing system 100 derives the positional deviation correction amount (step S304). Next, it is determined whether or not correction is possible with the current correction amount. For example, when the image of the registration mark is not normally formed, or when a proper check cannot be performed due to scratches on the intermediate transfer belt 41, no correction is made (step S305; N).

  If correction is possible without the above factors (step S305; Y), correction is performed in units of pixels (step S306). Here, with the K color image position as a reference, the formation positions of the other color images are corrected in units of pixels. The misregistration correction amount derived in step S304 includes a correction amount less than a pixel unit, but only the pixel unit portion is corrected in the first stage correction. For example, when the derived positional deviation correction amount is 4.68 dots, correction of 4 dots that is the pixel unit portion (integer portion) is executed. The pixel unit correction is performed by changing the values of the main scanning position correction signals 127Y, 127M, 127C, and 127K to be supplied to the pixel unit correction units 112Y, 112M, 112C, and 112K. This correction is completed immediately only by setting values in the pixel unit correction units 112Y, 112M, 112C, and 112K.

  Next, it is determined whether or not registration mark creation and measurement are repeated (step S307). If it is determined in step S305 that “no correction (N)” continues to be an error for a plurality of times or if the amount of misalignment correction falls within the target range, the first stage correction is not performed without repeating registration mark creation. And the process proceeds to the second stage (step S307; N). If no error occurs and the positional deviation correction amount does not fall within the target range (step S307; Y), the process returns to step S301, and registration mark creation / measurement is executed again. That is, when the amount of positional deviation correction does not fall within the target range, the next registration mark is created after correction in units of pixels.

  In the second-stage correction, it is determined whether or not the first-stage correction operation has ended normally without error (step S308). If there is an error (step S308; N), the correction operation ends with an error. When the first stage is normally completed (step S308; Y), correction including less than a pixel unit is performed (step S309), and a series of correction operations is ended (END). For example, in the case where the target range is 2 pixels and the positional deviation correction amount obtained by finally creating and measuring the registration mark is 1.6 dots, 1 pixel which is the pixel unit portion in step S306 In step S309, the remaining 0.6 dots are corrected.

  Correction less than a pixel unit is performed by changing the values of the surface phase control signals 122Y, 122M, 122C, and 122K supplied from the data processing system 100 to the correction units 111Y, 111M, 111C, and 111K. Since this correction is performed by the surface phase control of the polygon mirror, the rotation of the polygon mirror is stabilized after the angle is changed by the values of the surface phase control signals 122Y, 122M, 122C, and 122K until the correction operation is completed. It takes a few seconds. When it is necessary to create the next test image, only the pixel unit correction that is completed in a short time is performed before that, and the correction operation is not performed for the pixel unit that requires a long time as described above. The creation of the next test image can be started immediately after the correction. In other words, the time required for one cycle of creating and measuring a test image, deriving a misregistration correction amount, and correcting based on the test image is shortened. Is repeated many times, the time required for completing a series of correction operations is shortened.

  Although the embodiments of the present invention have been described with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention can be changed or added without departing from the scope of the present invention. include. For example, in the embodiment, correction is performed in units of pixels in step S306, and then correction in units of pixels is performed in step S309. After confirming that the amount of misalignment correction is within the target range, Depending on the correction amount, correction in pixel units and correction in less than pixel units may be performed simultaneously.

  In the embodiment, the case where the positional deviation of each color image in the main scanning direction is corrected has been described. However, the present invention can also be applied to correction in the sub-scanning direction and the like. In other words, when the correction operation can be performed separately into the first correction operation and the second correction operation that requires more time and fine correction, a short time is required before the next test image is created. It is only necessary to configure so that only the first correction operation that ends in step S1 is performed.

1 is a block diagram showing a configuration of a circuit portion related to color misregistration correction in an image forming apparatus according to an embodiment of the present invention. 1 is an explanatory diagram illustrating a cross-sectional configuration of an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing which shows a mode that a laser beam is reflected on a polygon mirror and scans a photoreceptor. 1 is an explanatory diagram illustrating a schematic configuration of a portion related to color misregistration correction in an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing which shows the polygon mirror of the state by which surface phase control was carried out. FIG. 6 is an explanatory diagram illustrating an example of a registration mark formed on an intermediate transfer belt. It is explanatory drawing which shows a mode that the position shift and lateral magnification of each color image are determined from a registration mark. 5 is a flowchart showing a color misregistration correction operation performed by the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

C ... Secondary transfer location 10 ... Image forming device 20 ... Automatic document feeder 21 ... Document loading tray 22 ... Paper feed roller 23 ... Contact roller 24 ... Guide roller 25 ... Switching claw 26 ... Reverse roller 27 ... Paper discharge tray 30 Reading unit 31 Contact glass 32 Platen glass 33 Light source 34 Mirror 35 Exposure scanning unit 36 Line image sensor 37 Condensing lens 38 Mirror 40 Printer unit 41 Intermediate transfer belt 42 Fixing device 43a 43b ... Registration sensor 44 ... Cleaning device 50Y, 50M, 50C, 50K ... Image forming unit 51Y, 51M, 51C, 51K ... Photoconductor 52Y, 52M, 52C, 52K ... Charging device 53Y, 53M, 53C, 53K ... Developing device 54Y , 54M, 54C, 54K ... cleaning devices 55Y, 55M, 5 C, 55K ... Laser unit 56Y ... Laser diode 57Y, 57K ... Polygon mirror 70 ... Paper feed means 71 ... Paper feed cassette 72 ... First paper feed roller 80 ... Conveyance means 80a ... Normal path 80b ... Reverse path 81 ... Conveyance roller 90 ... Control circuit 100 ... Data processing system 101 ... Control means 102 ... Test image creation means 103 ... Position detection circuit 104 ... Correction amount derivation means 110Y, 110M, 110C, 110K ... Correction means 111Y, 111M, 111C, 111K ... Less than a pixel unit Correction unit 112Y, 112M, 112C, 112K ... Pixel unit correction unit 121Y, 121M, 121C, 121K ... Polygon CLK
122Y, 122M, 122C, 122K ... plane phase control signal 123Y, 123M, 123C, 123K ... LD drive signal 124 ... CLK signal 125Y, 125M, 125C, 125K ... image signal 126Y, 126M, 126C, 126K ... H-START signal 127Y 127M, 127C, 127K ... main scanning position correction signal 200C ... C color registration mark 200K ... K color registration mark 200M ... M color registration mark 200Y ... Y color registration mark 211C, 211K ... first line element in the width direction 212C, 212K ... diagonal first line element

Claims (11)

In an image forming apparatus that includes a plurality of image forming units that form images of different colors, and forms a color image by superimposing a plurality of images of each color formed on the same image forming medium.
A test image creating means for creating a test image on the image forming medium for correcting a positional deviation between the images of the respective colors;
A correction amount deriving unit that measures a test image created on the image forming medium and derives a displacement correction amount between the images of the respective colors;
Correction means for correcting the image forming position by each of the image forming means;
Control means for controlling a series of correction operations for correcting the positional deviation between the images of the respective colors,
The control means performs the correction operation in a first stage and a second stage thereafter, and corrects the positional deviation in units of pixels until the positional deviation correction amount enters a predetermined target range in the first stage. Then, in the second stage, the positional deviation is corrected including a correction amount less than a pixel unit. In the first stage, the control means derives a correction amount by creating and measuring the test image, and in the second stage, based on the correction amount remaining without being processed in the first stage. The image forming apparatus according to claim 1, wherein correction is performed. In an image forming apparatus that includes a plurality of image forming units that form images of different colors, and forms a color image by superimposing a plurality of images of each color formed on the same image forming medium.
A test image creating means for creating a test image on the image forming medium for correcting a positional deviation between the images of the respective colors;
A correction amount deriving unit that measures a test image created on the image forming medium and derives a displacement correction amount between the images of the respective colors;
Correction means for correcting the image forming position by each of the image forming means;
Control means for controlling a series of correction operations for correcting the positional deviation between the images of the respective colors,
The control means repeatedly creates and measures a test image and derives a misregistration correction amount and then corrects the image formation position based on the derived misregistration correction amount, and the derived misregistration correction amount is within a predetermined target range. Image formation is characterized in that image misalignment is corrected in units of pixels while the image is not within the range, and when the amount of misalignment correction is within the target range, the image formation position is corrected including a correction amount less than the unit of pixels. apparatus. The control means repeats the creation of the test image, the measurement of the test image, the derivation of the misalignment correction amount, and the correction of the image formation position while the misalignment correction amount is not within the target range. The image forming apparatus according to claim 3, wherein the positional deviation of the image is corrected in units of pixels. The image forming apparatus according to claim 3, wherein the control unit executes a correction including a correction amount less than the pixel unit and ends a series of correction operations. 6. The image forming apparatus according to claim 1, wherein the time required for correction in units of pixels is shorter than the time required for correction in units of pixels. The image forming apparatus according to claim 1, wherein the correction in less than a pixel unit is performed by surface phase control of a polygon mirror. In a color misregistration correction method in an image forming apparatus that includes a plurality of image forming units that form images of different colors and superimposes a plurality of images of each color formed on the same image forming medium to form a color image.
The correction of color misregistration is performed in the first stage and the subsequent second stage, and in the first stage, the misregistration is corrected in units of pixels until the misregistration correction amount between the images of the respective colors falls within a predetermined target range. A color misregistration correction method comprising correcting the misregistration including a misregistration correction amount less than a pixel unit in the second stage. In a color misregistration correction method in an image forming apparatus that includes a plurality of image forming units that form images of different colors and superimposes a plurality of images of each color formed on the same image forming medium to form a color image.
Creating a test image on the image forming medium for correcting misregistration between images of each color, measuring the test image, and deriving a misregistration correction amount between the images of each color; Repetitively performing in this order until the misregistration correction amount falls within a target range, correcting the misregistration between the images of the respective colors in units of pixels based on the misregistration correction amount;
And a step of correcting misregistration between the images of the respective colors including misregistration less than a pixel unit when the misregistration correction amount falls within a target range. 10. The color misregistration correction method according to claim 8, wherein the time required for correction in pixel units is shorter than the time required for correction in less than pixel units. The color misregistration correction method according to any one of claims 8 to 10, wherein correction less than a pixel unit is performed by surface phase control of a polygon mirror.

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